The confocal miniprobe (Cell-viZio-GI) used in Specific Aim 2 provides horizontal cross-sectional images up to 100 (im tissue penetration depth. This distance is insufficient to assess for the presence of neoplastic invasion and micrometastases below the muscularis mucosa (Fig 3b), which is needed to accurately stage the progression of cancer. We have achieved vertical cross-sectional images with 500 ^m tissue penetration depth ex vivo using the novel dual axes confocal architecture (Fig 8b). This orientation is preferred :for pathological evaluation because it reveals the natural growth and proliferation of tissue micro-structures. Furthermore, we have developed a 5 mm diameter (endoscope compatible) dual axes prototype that achieves high speed scanning in the horizontal (xy-) plane using a MEMS (micro-electro-mechanical sytems) mirror. In order to achieve vertical cross-sections, we need to develop an axial (z-) scanner that performs with sufficient speed for in vivo imaging. MEMS actuators have been developed previously for a number of applications, including computer hard drives,82'83 aviation fluid control systems,84 and optical fiber manipulators.85 These designs are based on electrostatic, thermal, or electromagnetic principles. Howev.er, each of these approaches have limitation in either the amount of force that can be generated or by the size and power required to move the scanhead over the desired range of motion. Pneumatic actuation offers a reliable, robust approach for axial displacement that provides many of the features needed to meet in the in vivo scanning requirements, including 1) high power/force density, 2) large motion displacement, 3) design flexibility, and 4) variety in choice of driving medium. The actuation speed is inherently less than that for MEMS-based electrostatic, thermal, and electromagnetic approaches, but a recent study has shown that pneumatic (air-driven) actuators can achieve axial motions as large as 300 urn at 5 Hz.86 This bandwidth is sufficient for the dual axes confocal microscope to achieve vertical cross-sectional images of 500 jam penetration depth using 785 nm light.